Offshore wells may be pre-drilled to minimize downtime of a production platform before the well produces hydrocarbons. A drilling template is installed on the seabed and a drilling rig (e.g., a jackup rig) is positioned over the drilling template. A mudline suspension system is installed when drilling. The mudline suspension system comprises a series of concentric mudline hangers (e.g., one for each casing string) and an internal profile to receive a hanger. The mudline hangers are used to support casing string weight at the mudline. On completion of drilling, abandonment caps can be run into the mudline system to seal and plug the well.
Subsequently, a production platform is positioned over the drilling template and tieback strings may be stabbed into the mudline suspension system, by means of tieback tools at the lower end of each tieback strings, to extend the casing conduits back to a wellhead on the platform. Once the casing strings have been tied back to the surface, the tubing completion string is run and well production may begin after perforation.
Wells typically require running of several concentric casing strings. The innermost casing string, which receives the completion tubular, is called the production casing. This string typically extends into the hydrocarbon bearing zone, and is therefore required to be of high integrity.
Traditional stab-in solutions for coupling the production casing tieback tool to the production casing mudline hanger require that sections of the production casing tieback tool have a reduced wall thickness to accommodate coupling mechanisms. This reduced wall thickness is unacceptable for high-pressure, high-temperature (“HPHT”) applications. As a result, the above-described method of pre-drilling offshore wells to the production casing stage is not suited for use in HPHT applications and the efficiencies resulting from pre-drilling offshore wells are not fully realized in HPHT applications.